The present invention relates to gas turbine engine casings, and more particularly to fan casings made of composite material for gas turbine aeroengines.
In a gas turbine aeroengine, the casing has a portion forming an air inlet sleeve with the function of defining the air inlet passage into the engine, and a portion forming a fan casing. A particular function of the fan casing is to retain debris, such as articles that have been ingested or fragments of damaged blades, which debris is projected by centrifugal force and needs to be prevented from passing through the casing and reaching other portions of the aircraft. The fan casing also supports a certain number of pieces of equipment of the engine, such as harnesses for fastening pipes conveying de-icing liquid or supports for fastening the electronic control unit of the engine.
In known manner, the air inlet sleeve and the fan casing have annular flanges at their axial ends serving in particular to mount the air inlet sleeve on the fan casing. For this purpose, the adjacent flanges of the air inlet sleeve and of the fan casing are generally fastened together by means of a plurality of nut-and-bolt type fastener systems distributed all around their circumference. The upstream flange of the fan casing is also used for fastening pieces of equipment that are supported by the casing, with this fastening also being provided by means of fastener bolts that pass through the upstream flange.
In order to enable pieces of equipment to be removed without it being necessary to begin by removing the air inlet sleeve, the flange of the air inlet sleeve generally presents festoons that receive the heads of the bolts for fastening pieces of equipment on the upstream flange of the fan casing. These festoons thus give easy access to the bolts for fastening pieces of equipment and enables them to be withdrawn it being necessary to begin by removing the air inlet sleeve.
Furthermore, it has become common practice to make the air inlet sleeve of the casing out of composite material of the fibers-and-resin type by making a fiber preform, impregnating it with a resin, and molding in order to obtain the desired shape directly.
Unfortunately, making festoons in the flange of an air inlet sleeve made out of composite material in order to be able to remove pieces of equipment leads to fibers being cut in the circumferential direction, thereby considerably weakening the circumferential mechanical strength of the air inlet sleeve.